Over the past two decades, information about the role of eosinophils in human disease has dramatically increased. The eosinophil is not a bystander cell but rather an active participant in a spectrum of pathophysiologic events, such as inflammatory responses in the lung, skin, and heart. The evidence now available suggests that elaboration of inflammatory mediators by eosinophils plays a critical role in the pathophysiological mechanisms of diseases. However, little information is available regarding how eosinophil degranulation occurs in human diseases. Cytokines are now known to play a crucial role in inflammatory responses by modulating the number and function of involved cells. Although the production of these cytokines by activated T lymphocytes and mast cells is well documented, the potential of eosinophils as cytokine- producing cells is not yet fully elucidated. This project focuses on the mechanism of eosinophil activation in human diseases. We will investigate the factors which induce the release of granule proteins and production of cytokines from eosinophils. Three goals are identified. First, models of IgE-mediated eosinophil degranulation in vitro will be established and investigated by co- incubation of eosinophils with anti-IgE- or allergen-stimulated peripheral blood mononuclear cells, dispersed skin cells, and bronchoalveolar lavage cells. We will dissect the critical elements needed for eosinophil degranulation and explore the nature of the molecules involved in these interactions. Second, stimulants and modulators of eosinophil degranulation in vitro will be identified by testing a variety of molecules as possible secretagogues for eosinophils, including immunoglobulins, complement components, lipid mediators, and cytokines. Once secretagogues are identified, the factors will be studied as potential modulators of eosinophil degranulation in vitro. This goal complements the analyses of IgE-mediated eosinophil degranulation because it identifies the essential stimuli for eosinophil activation and allows us to increase the complexity of the in vitro conditions to reconstitute the system to mimic eosinophil degranulation in vivo. Third, the capacity of eosinophils to produce cytokines will be examined by stimulating eosinophils with secretagogues, and by detecting cytokines as mRNA and released protein. The importance of eosinophil heterogeneity in cytokine expression will be studied by using eosinophils from patients with asthma and eosinophilia and comparing these cells to eosinophils from normal persons. This project is related to Project 1, "Mechanism of Eosinophil and Vascular Interactivity", which dissects the importance of eosinophil adhesion and migration on eosinophil activation. We believe these studies will lead to a better understanding of the mechanism of eosinophilic inflammation and the physiological role for eosinophils in allergic and immune responses.